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The Practical Pumping Handbook ...........................................................................................................................................
Figure 8.7: Paper stock pump (Reproduced with permission of Sulzer Pumps)
(A.D.) consistency is an arbitrary convention used by papermakers, and
is the amount of pulp left in a sample after drying in atmosphere. Air
Dry stock contains 10% more moisture than Bone Dry stock, i.e., 6%
B.D. is 6.6% A.D. Air Dry consistency is the term most commonly
used, and it will be used throughout this discussion unless otherwise
noted.
The consistency can range between 0.1% up to about 20%, but only
starts to become a pumping problem when it reaches the 3% level. Up
to that point, pump performance can be considered to be like water. As
the consistency increases, pump performance will decrease rapidly.
Between 3% and 6% consistency, correction factors are traditionally used
for the performance of a centrifugal pump, as discussed in Chapter
8.2.5.
8.2.1 Air in stock
Entrained air is detrimcntal to good operation of any centrifugal pump,
and can result in reduced capacity, increased erosion and shaft breakage.
Obviously every effort must be made to prevent the over-entrainment
of air throughout the process.
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